1. Field of the Invention
The present invention relates to a semiconductor acceleration sensor used for an industrial-robot attitude control system or an automobile suspension control system.
2. Description of the Related Art
FIG. 4 is a sectional view taken along line 4--4 of FIG. 5 showing an existing semiconductor acceleration sensor. FIG. 5 is a top view of the existing semiconductor acceleration sensor with its cover removed. A plurality of outer leads 11 are soldered, by means of dipping, at a thick-film substrate 7, a ceramic rectangular thin plate. This circuit substrate includes a thick-film circuit in order to transfer an electrical signal outside of the sensor. A rectangular parallelepiped pedestal 4 made of silicon is secured to the thick-film resistance substrate 7 by an epoxy-based adhesive 9. An end of a slender acceleration detecting beam 2 is secured to the pedestal 4 as a cantilever with the epoxy-based adhesive 9. A cover 12 is arranged on the thick-film resistance substrate 7 so as to cover electronic parts arranged on the substrate 7 and the margin of the cover 12 is bonded to the circumference of the thick-film resistance substrate 7 with a silicon based adhesive 13.
The acceleration detecting beam 2 is a flexible beam supported by the pedestal 4 and deflects in accordance with applied acceleration. A sensor device 1 converts the deflection of the beam into an electrical signal and is located almost at the center of and on the acceleration detecting beam 2. The sensor device 1 comprises a bridge circuit (not shown) including a gauge resistor using the piezo-resistance property of a semiconductor material.
Moreover, an amplification circuit 15 for amplifying an electrical signal generated by the sensor device 1 is formed on the acceleration detecting beam 2. To transfer an electrical signal output from the amplification circuit 15 to a temperature compensation circuit 16 on the thick-film substrate 7, a wire (not shown) formed on the acceleration detecting beam 2 by means of diffusion and an Au wire 10 serving as a conductor are arranged between the amplification circuit 15 and the temperature compensation circuit 16.
The temperature compensation circuit 16, which is a thick-film circuit, is formed on the thick-film substrate 7 in order to compensate the temperature characteristic of an electrical signal output from the amplification circuit 15. The temperature compensation circuit 16 comprises a thick-film resistor 5 made of ruthenium oxide (RuO.sub.2, Ru.sub.2 O.sub.5) and a circuit conductor 6 made of printed silver palladium (Ag--Pd) or silver platinum (Ag--Pt) which are printed on the thick-film resistor substrate 7. Moreover, the thick-film resistor 5 and the circuit conductor 6 are covered with over-glass 8 made of lead borosilicate glass (PbO--B.sub.2 O.sub.3 --SiO.sub.2) as an insulating layer in order to protect the resistance 5 and the conductor 6.
This type of the semiconductor acceleration sensor makes it possible to convert a very small acceleration into an electrical signal by using the piezo-resistance property of the sensor device 1 due to deflection of the acceleration detecting beam 2. Moreover, the sensor makes it possible to amplify an electrical signal generated by the bridge circuit 1 with the amplification circuit 15 and compensate the temperature characteristic of the electrical signal with the temperature compensation circuit 16 and thereafter output the signal to the outside of the sensor through the outer leads 11.
In the case of the existing semiconductor acceleration sensor thus constituted, the silicon pedestal serving as a support for forming the acceleration detecting beam 2 as a cantilever structure is formed by fixing rectangular parallelepiped components made of silicon with the epoxy-base adhesive 9. Therefore, a lot of materials and a lot of fabrication processes are required.
The present invention is made to solve the above problems and its object is to provide a reliable inexpensive semiconductor acceleration sensor requiring no special material as a pedestal and making it possible to decrease the number of materials and the number of assembling processes.